Our overall goal is to perform experiments which will advance our knowledge and understanding of protein turnover and of the membrane transport of amino acids in the lung and of factors which influence and regulate these processes. We shall use the isolated perfused rat lung to study 1) the turnover (synthesis and degradation) of general and specific (angiotensin converting enzyme and superoxide dismutase) proteins, 2) the membrane transport of amino acids and 3) the associated changes in organelles (rough endoplasmic reticulum, smooth endoplasmic reticulum, lysosomes) of cells of the alveolar air-tissue interface. We anticipate that these experiments will generate information which will enlarge our understanding of the molecular and cellular basis of lung function at the organ level, provide data which will shed light on developmental and reparative processes of the lung and develop knowledge useful to our understanding of the molecular and cellular response of the lung to alterations in its normal condition. We expect to achieve these goals using biochemical and ultrastructural morphometric techniques. It must be stressed, however, that we are using these techniques on the lung because we are interested in the behavior of this organ and not because the lung affords a convenient model for the study of the fundamental biological processes involved.